Currently, commonly used commercial scale production of hydrogen peroxide is based on an auto oxidation process employing alkyl anthraquinone as the working material. This process involves reduction of alkyl anthraquinone dissolved in an organic working solution to alkyl anthraquinol. The alkyl anthraquinol is oxidized by air to produce hydrogen peroxide and alkyl anthraquinone, which is recycled in this process. This process comprises a number of operations involving reduction, oxidation, separation by aqueous extractions, refining and concentration, making the process complex. Apart from the requirements of high capital and operation costs, this process has following limitations and disadvantages:                Non-selective in hydrogenation, hence loss of anthraquinone.        Difficulties in separation hydrogenation catalyst and degradation products.        Need for the regenaration of used hydrogenation catalyst.        Need for the removal of organic matters from the extracted H2O2 solution.        Waste treatment and disposal of undesired side products of the cyclic process.        
Demand for hydrogen peroxide has been continuously increasing in the field of oxidation of organic compounds to value added products, wastewater treatment and water disinfection. Hence, there is a great practical need for replacing the anthraquinone process by an environmentally clean and more economic process such as a direct partial oxidation of hydrogen by oxygen to hydrogen peroxide with high conversion and selectivity.
Since the disclosure in U.S. Pat. No. 1,108,752 by Henkel et al. that palladium is a catalyst promoting the formation of hydrogen peroxide and water from a mixture of hydrogen and oxygen, a number of palladium containing catalysts, useful for the direct oxidation of hydrogen by oxygen to hydrogen peroxide, are disclosed in several granted patents and patent applications.
U.S. Pat. No. 4,832,938 by Gosser et al. discloses a Pt—Pd bimetallic catalyst supported on a carbon, silica or alumina support for making hydrogen peroxide from a direct combination of hydrogen and oxygen in an aqueous reaction medium. German Patent Ger. Offen. GE 4127918 A1 by Lueckoff et al. discloses a supported palladium gold catalyst for the manufacture of hydrogen peroxide from hydrogen and oxygen in an aqueous medium; the catalyst contains 5-95 wt % Au and is supported on carbon. A number of platinum Group metal containing catalysts: (1) Pt-group metal on high surface area support, such as carbon, silica or alumina (Ref. U.S. Pat. No. 5,169,618); (2) Pt-Group element supported on solid acid carrier (Ref. Eur. Pat. Appl. EP 504,741, A1); (3) Pt-Group element supported on Nb- or Ta oxide (Ref. PCT Int. Appl. WO 9412428 A1); (4) Sn-modified Pt-Group metals supported on catalysts carriers (Ref. Eur. Pat. Appl. EP 621,235 A1); (5) Pt-Group metals supported on hydrophilic support (Ref. U.S. Pat. No. 5,399,334); for the oxidation of hydrogen to hydrogen peroxide are known in the prior art.
Japanese Patent Jpn. Kokai Tokkyo Koho JP 01133909 A2 by Kyora discloses a Pt-Group metal catalyst carried on a hydrophobic support such as porous and hydrophobic Teflon support. European Patent EP 366419 A1 discloses a Group VIII metal catalyst deposited on a hydrophobic support for the manufacture of hydrogen peroxide by reacting hydrogen with oxygen in an aqueous medium. WO 93/14025 A1 teaches a Group VIII metal deposited on a partially hydrophobic and partially hydrophilic support, such as Pd on fluorinated carbon, as a catalyst for the oxidation of hydrogen-to-hydrogen peroxide.
While there are several disclosures regarding the formation of hydrogen peroxide, the applicants herein are unaware of any practice relating to the direct oxidation of hydrogen-to-hydrogen peroxide for the production of hydrogen peroxide. One reason for this is the poor hydrogen peroxide selectivity and yield observed in this process.
Choudhary et al. in U.S. Pat. No. 6,534,440 disclose a process for the activation of a catalyst comprising metallic palladium, useful for the direct oxidation of hydrogen by oxygen to hydrogen peroxide, which comprises treating the catalyst with an oxidizing agent, preferably selected from perchloric acid, hydrogen peroxide, nitrous oxide and oxygen or air, such that not only a surface oxidation but also at least a partial bulk oxidation of the metallic palladium, present in the catalyst, to palladium (II) oxide (PdO) occurs; and optionally calcining the treated catalyst at a temperature in the range from about 50° C. to about 500° C. However, the increase in the hydrogen peroxide selectivity and/or yield by this method is small.
U.S. Pat. Nos. 4,681,751; 4,772,458; 4,889,705; 5,135,731 of Gosser et al. disclose the use of halide promoters added to acidic liquid reaction medium employed for the direct oxidation of hydrogen to hydrogen peroxide over a metallic catalyst for improving the hydrogen peroxide yield in the process. However, because of the presence of halide anions, the acidic liquid reaction medium becomes highly corrosive, limiting the use of halides in the liquid medium for the purpose of improving selectivity or yield of hydrogen peroxide in the process.
It is therefore of importance to develop a method, which overcomes the limitations of the earlier methods, for drastically improving both the selectivity and yield of hydrogen peroxide in the direct oxidation of hydrogen by oxygen to hydrogen peroxide.